I know it's an old thread but I think it will be useful for someone else. I solved the FPS and CPU usage issue. It's not perfect but it's way better now. The solution was simple: instead of destroying and creating instance each time there is an HP change, I figured it was easier to turn visible/invisible the HP bar pieces. It's easily configurable so you guys can experiment with different values. Have fun!
Thanks to all of you for your work. Special thanks to zyblade, Jayjay and zenox98 (I sadly was not able to see/test others previous links).